An escalator, and other similar types of passenger conveyors such as moving walks, generally include a passenger supporting moving walkway and a pair of handrails which move generally in synchronism with the walkway. The individual steps of the escalator are conveyed typically by means of an endless chain at a generally constant speed. While the handrails are intended to move at the same speed as the passenger support and transport mechanism, this is not always the case. For example, installation variations and mechanical tolerances of the various components may cause the handrails to operate at a slower speed than the support/transport mechanism. In addition, changes in the environment as well as the extent of usage frequently result in handrail speed variation. For example, the cotton fibers used in most handrails are responsive to changes in temperature and humidity giving rise to changes in handrail tension. Changes in handrail tension, in turn, cause handrail slippage and speed reduction. Handrail slippage also causes excessive handrail wear because most handrails are frictionally driven requiring frequent replacement. In addition, handrails tend to stretch with use and particularly with abuse. Such abuse may take the form of either pulling on the handrail or engaging the handrail with an object for the purpose of either temporarily or permanently interrupting handrail operation.
Changes in handrail speed with respect to the speed of the transport/support mechanism can be dangerous, particularly in the case of escalators. When moving upward, slower displacement of the handrails causes one to lean rearward, sometimes resulting in a loss of balance and a dangerous fall down the escalator. Slower movement of the handrails as the escalator moves downward also frequently causes one being transported to lose his or her balance and fall on the sharp edged stairs. Even in a generally horizontal moving walk, a speed differential between the support/transport mechanism and the slower handrail frequently causes one to lean rearward resulting in a loss of balance and a potentially dangerous fall, particularly in the case of the elderly and infirm.
Prior attempts to eliminate the hazard of slow moving handrails have addressed only a complete failure of the handrail transport system resulting in its stopping. In response to handrail stoppage, prior approaches have provided for the automatic shutdown of the escalator to prevent serious injury. In fact, continuous slippage of the handrails is frequently more dangerous than complete stoppage because a slipping handrail tends to lull the passenger into a false sense of security as he or she rests upon the handrail, resulting in an ever increasing displacement between the passenger's feet and hands. Suddenly, the passenger is in an awkward position, loses his or her balance, and falls down to the walkway. Moreover, slippage causes deterioration of the handrail to the point that the handrail is usually seriously damaged when its motion is completely interrupted.